Absorbent personal care articles such as sanitary napkins, disposable diapers, incontinent-care pads and the like are widely used, and much effort has been made to improve the effectiveness and functionality of these articles. These articles generally include a liquid absorbent material backed by a liquid-impervious barrier sheet. To enhance the sense of comfort, the absorbent material has a facing of a material which masks at least the body-facing surface of the product. The purpose of this cover material is to help structurally contain the absorbent material and to protect the wearer from continuous direct contact with moisture from previously wetted absorbent material. The cover material is typically a relatively low basis weight nonwoven fabric. Improved product performance has been obtained in these products through the incorporation of a surge management material disposed between this cover material and the absorbent material. (See U.S. Pat. No. 5,429,629.) The surge management material is made from a relatively high basis weight, low density, that is thick, nonwoven web material. The cover material must, therefore, be permeable to liquids on the side of the product that is placed against the body, actively promoting the immediate transfer of each liquid application or insult through the surge management material and into the absorbent pad. It is also necessary that the surge management material initially hold the liquid passed through the cover material and then give up said liquid to the absorbent material.
In order to satisfy these requirements, it is necessary that the surfaces of the cover material and surge management material or the surface of the fibers forming said nonwoven fabrics, be first wetted by the liquid. Wettability of nonwoven webs or fibers thereof is known to be achievable by treating the surface thereof with surfactants. See, for example, U.S. Pat. No. 4,413,032 to Hartmann et al. and U.S. Pat. No. 5,045,387 to Schmalz. Alternative methods of imparting wettability to such materials are taught, for example, by U.S. Pat. No. 5,456,982 to Hansen et al. in which a bicomponent fiber is provided with permanent hydrophilic surface properties by incorporating a surface active agent into the sheath component and optionally by including a hydrophilic polymer or copolymer in the sheath component. See, also, U.S. Pat. No. 5,582,904 to Harrington which teaches the incorporation into a polyolefin-containing cast or spin-melt composition for production of nonwoven materials a modifier composition comprising at least one M,M-polyalkoxylated 10-22 carbon fatty acid amine, inclusive of amines having 12-20 carbon and preferably 18 carbon linear straight chain moiety corresponding to that found in stearic or oleic acid, and up to about 60%, including 0.1%-45% by weight of a modifier composition, of a primary or secondary 10-22 carbon fatty acid amide, such as stearamide.
We have found, however, that the use only of internal surfactants, which without a subsequent blooming step impart instantaneous wettability, results in fabrics that are not durable to multiple insults. By durability, we mean the ability of the material to withstand multiple insults. We have also found that a high basis weight, low density polyolefin web with an internal surfactant is desirable for improving treatability by a topical surfactant in order to provide good wettability. Fabrics without an internal surfactant, but which are topically treated with dilute solutions of surfactants, also exhibit good wettability. However, this approach is undesirable because a significant amount of drying is required.
Accordingly, it is one object of this invention to provide a nonwoven web material having improved durability and processability over conventional nonwoven materials treated with internal or topical surfactants alone.
It is another object of this invention to provide a dual treatment system, that is one employing both internal and topical surfactants, for improving the durability and processability of nonwoven web materials.
It is yet another object of this invention to provide a nonwoven web material which is instantaneously wettable so as to provide virtually instantaneous transport of liquids through the web.